Reflection seismic profiles of the core‐mantle boundary
Reflection seismic profiles of the core‐mantle boundary
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核幔边界反射地震剖面
DOI：
10.1029/2003jb002515
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发表时间：
2004
影响因子：
--
通讯作者：
L. N. Solidilov
中科院分区：
文献类型：
--
作者：
A. Ross;H. Thybo;L. N. Solidilov
[1]在西伯利亚和平核爆炸资料上观测到来自核幔边界（CMB）的高振幅、高频和横向相干地震相。这些到达的观测距离为2600-4000公里，与CMB反射（PcP）一致的移动时间和移动时间相抵消，并且由于10公里的站点间隔很小，因此很容易相互关联。到达的持续时间和复杂性与单一CMB接口的简单反射不一致。尽管地震记录表明西伯利亚这部分地区下面不存在超低速带，但它们需要超低速带顶部的PcP和复杂前驱相（PdP）的结合。波形的横向变化表明，在150-200 km的波长和高达8 km的振幅范围内，ULVZ的厚度和物理性质发生了变化。我们发现至少有一个地方没有ULVZ。在另一个采样良好的位置，前驱体的频率含量高于初级到达。这些PcP/PdP相位的反射率建模表明，在ULVZ中可能需要千米尺度的分层来解释地震波形和频率分裂。模拟结果表明，在极低频区，纵波和横波的速度分别降低了25%和40%。这表明极空区部分熔体的百分比比迄今所解释的要高。我们的观测表明，极低频区可能存在于地球的广大区域，其厚度低于频率含量较低的地震资料的分辨率极限。
[1] High amplitude, high frequency, and laterally coherent seismic phases from the core-mantle boundary (CMB) are observed on data from Peaceful Nuclear Explosions in Siberia. These arrivals are observed at 2600–4000 km offset with travel times and move-outs consistent with CMB reflections (PcP) and are readily correlated because of the small station interval of 10 km. The duration and complexity of the arrivals are inconsistent with a simple reflection from a single CMB interface. They require the combination of PcP and a complex precursor phase (PdP) from the top of an ultralow-velocity zone (ULVZ) despite the fact that earthquake recordings indicate that there is no ULVZ present beneath this part of Siberia. Lateral variations in the waveform imply that the thickness and physical properties of the ULVZ change with a wavelength of 150–200 km and an amplitude of up to 8 km. We find at least one location where there is no ULVZ present. At another well-sampled location, the precursor has higher frequency content than the primary arrival. Reflectivity modeling of these PcP/PdP phases shows that kilometer-scale layering may be required in the ULVZ to explain the seismic waveform and the frequency split. The modeling shows very low velocity in the ULVZ with reductions of 25 and 40% for P and S waves, respectively. This indicates higher percentages of partial melt in the ULVZ than hitherto interpreted. Our observations indicate that the ULVZ may be present over wide areas of the Earth with a thickness below the resolution limit of seismological data with a lower frequency content.